JP-B-2800981 discloses a technique for measuring the concentration of a particular component in a sample such as blood. The prior art is an electrochemical method utilizing a biosensor incorporating a reagent layer and a pair of electrodes. According to the method, a sample is introduced to the reagent layer of the biosensor, with a voltage applied across the paired electrodes, and then the current between the electrodes is measured. Immediately after the sample is introduced to the reagent layer, the current increases as the electrodes and the reagent layer become wet. Thus, the introduction of the sample to the regent layer can be detected based on the fact that the current has reached a predetermined threshold. The component in the sample undergoes reaction with a component in the reagent layer, and the current will change depending on the degree of the reaction. The degree of the reaction depends on the concentration of the particular component in the sample. Therefore, it is possible to calculate the concentration of the particular component in the sample, based on the detection of the current performed when a certain period of time has passed from the preset reference time point, i.e., the time point when the current reaches the predetermined threshold.
To conduct such an analysis, it is desirable that the biosensor to be used is subjected to properness or improperness checking. This is because the user of the analyzer does not always use a proper biosensor. For example, use may be made of a biosensor which was once used, or one which has been unused (exposed) for a long time with its package opened, or one which has undergone the deterioration of the components of the reagent layer because a prolonged period of time has lapsed since the sensor was produced. When the analysis is carried out without finding the user's erroneous use of such an improper biosensor, accurate analysis results cannot be obtained and the analysis itself is useless. Further, the user may mistake such inaccurate analysis results for accurate ones.
No means of performing accurate checking for improper sensors has been proposed so far. The above-mentioned JP-B-2800981 teaches means for detecting an insufficient supply of a sample to the reagent layer. However, it is difficult to accurately detect the improperness of the biosensor by such means.